The blackening of the glans and the coronal groove may be caused by physiological factors, acute injuries, circumcision and glansitis. 1. Physiological factors: age and prolonged masturbation may lead to the glans and coronal groove pigmentation, may make the glans and the coronal groove become darker, there is no other clinical manifestations, do not have to worry too much. 2. Acute injury: the penile area suffered an acute injury, may need to be pressurized bandage, bandage is too tight resulting in local blood flow, may make the glans will be black, should be re-visit the doctor for bandage. 3. circumcision glans: may be related to poor hygiene, repeated occurrence of circumcision glans, by inflammatory stimulation, may make the glans coronal groove black, may also be accompanied by itching, pain and other symptoms. The glans is black and there are other abnormal manifestations, excluding physiological factors, it is recommended to consult a doctor for examination and treatment.